Observer pattern in PHP - Mini Project: Build & Apply

Observer pattern

📖 Scenario: You are building a simple notification system where a NewsPublisher sends news updates to multiple Subscribers. When the publisher has new news, all subscribers should be notified automatically.

🎯 Goal: Create a basic Observer pattern in PHP where a NewsPublisher notifies multiple Subscribers when news is published.

📋 What You'll Learn

Create a NewsPublisher class that holds news and a list of subscribers.

Create a Subscriber class that can receive news updates.

Implement methods to add subscribers to the publisher.

Notify all subscribers when new news is published.

Print the news received by each subscriber.

💡 Why This Matters

🌍 Real World

Observer pattern is used in real apps to update parts of a program automatically when something changes, like notifications, event handling, or UI updates.

💼 Career

Understanding Observer pattern helps in building scalable and maintainable software, especially in event-driven programming and frameworks.

1

Create the NewsPublisher class with a subscribers array

Create a class called NewsPublisher with a public property subscribers initialized as an empty array.

PHP

<?php

// Create the NewsPublisher class with a public subscribers array

# Your code here

Need a hint?

Use public array $subscribers = []; inside the class to hold subscribers.

2

Create the Subscriber class with a name property

Create a class called Subscriber with a public property name. Add a constructor that accepts a string $name and sets the name property.

PHP

<?php

class NewsPublisher {
    public array $subscribers = [];
}

// Create the Subscriber class with a name property and constructor

# Your code here

Need a hint?

Use public string $name; and a constructor to set it.

3

Add methods to NewsPublisher to add subscribers and notify them

In the NewsPublisher class, add a public method addSubscriber(Subscriber $subscriber) that adds the subscriber to the subscribers array. Also add a public method notifySubscribers(string $news) that loops over subscribers and calls a receiveNews(string $news) method on each subscriber.

PHP

name = $name;
    }
}

Need a hint?

Use $this->subscribers[] = $subscriber; to add subscribers and a foreach loop to notify.

4

Create instances and test the notification system

Create a NewsPublisher instance called publisher. Create two Subscriber instances with names "Alice" and "Bob". Add both subscribers to publisher using addSubscriber. Call notifySubscribers on publisher with the news string "New PHP version released!". Print the output.

PHP

subscribers[] = $subscriber;
    }

    public function notifySubscribers(string $news): void {
        foreach ($this->subscribers as $subscriber) {
            $subscriber->receiveNews($news);
        }
    }
}

class Subscriber {
    public string $name;

    public function __construct(string $name) {
        $this->name = $name;
    }

    public function receiveNews(string $news): void {
        echo $this->name . " received news: " . $news . "\n";
    }
}

// Create instances and notify subscribers

# Your code here

Need a hint?

Create objects and call methods exactly as described to see the notifications.